How to build a 12v Battery Pack using Li-ion Cells

This project constructs a 12V 2000mAh lithium-ion battery pack by wiring three individual 18650 Li-ion cells in a series configuration. In a series arrangement, the nominal voltage of each cell (approximately 3.6V to 3.7V) adds together, resulting in a combined nominal output of roughly 11.1V to 12.6V when fully charged. To physically and electrically connect the cells, 0.15mm coated nickel strips are spot-welded across the battery terminals, providing a low-resistance current path. Because lithium-ion chemistry requires strict voltage regulation to prevent damage, a 3S 6Amp Battery Management System (BMS) module is integrated into the circuit. The BMS connects via a JST XH 2.54 female 4-pin connector to monitor individual cell voltages, ensuring that the cells charge and discharge evenly while protecting the pack against over-charging, over-discharging, and excessive current draw. Finally, a barrel connector serves as the external power interface for connecting loads or chargers, and the entire assembly is sealed inside a 100mm PVC heat shrink sleeve for mechanical protection and insulation.